Spheroid-producing device, method for recovering spheroids, and method for producing spheroids

ABSTRACT

The present invention provides a device for producing a large number of uniform spheroids by an easy method. The spheroid-producing device ( 1 ) at least includes a first surface ( 11 ), a second surface ( 12 ), and a plurality of wall surfaces ( 13 ). The second surface ( 12 ) faces the first surface ( 11 ). The respective wall surfaces ( 13 ) constitute a plurality of holes penetrating through the first surface and the second surface. In addition, an equivalent diameter of inscribed circles of openings in the first surface ( 11 ) is greater than an equivalent diameter of inscribed circles of openings in the second surface ( 12 ).

TECHNICAL FIELD

The present invention relates to a device suitable for culturingspheroids with a uniform size in large numbers and in high density and amethod using the device.

BACKGROUND ART

Non patent literature 1 indicates that the three-dimensional culturemethod is available for reproducing the functions of living tissues moreaccurately than the two-dimensional culture method. Non patentliterature 1 also indicates that the three-dimensional culture method isone of methods useful for efficiently differentiating pluripotent stemcells and iPS cells. Attempts are being made to rebuild and complementlost functions by returning three-dimensionally cultured artificialtissues into a body using such a technique. Moreover, other attempts arebeing made to apply such a technique to regenerative medicine forassistance of damaged tissue repair. Further attempts are being made touse such a technique for testing toxicity of pharmaceutical agents. Inparticular, large-scale production of cell aggregates that are uniformin size and shape is required for regenerative medicine and itsresearch. In addition, a method with higher convenience and lower costthan existing methods will become necessary.

[Significance of Producing Uniform Sized and Shaped Cell Aggregates]

In the case of liver cells, there is a problem that in vivo functionscannot be reproduced in vitro. One example of this problem is that thedrug metabolism function inherent in liver cells is deteriorated whenthe liver cells are two-dimensionally cultured. One of means foraddressing this problem is a method for forming cell aggregates asdisclosed in Non-patent literature 2. Non patent literature 2 indicatesthat the function of the cell aggregates produced by this method isdramatically improved from those of the two-dimensionally culturedcells.

When embryonic stem cells or induced pluripotent stem cells aredifferentiated into target cells in vitro, cell aggregates calledembryoid bodies is formed, followed by the initiation of the program ofdevelopment and differentiation, to thereby differentiate embryonic stemcells or induced pluripotent stem cells into target cells. Non patentliterature 3 reports that size of cell aggregates influence thedirections of differentiation.

[Regarding Technique for Producing a Large Number of Uniform Size andShape Cell Aggregates]

Non patent literature 4 discloses a culture method called the hangingdrop method in which culture is performed in droplets. Non patentliterature 4 further discloses a U or V bottomed low adherence plate.Non patent literature 4 also discloses a large-scale culture methodusing bioreactors. The hanging drop method, U bottomed plate and thelike are suitable for producing cell aggregates that are uniform in sizeand shape. On the other hand, the hanging drop method, U bottomed plateand the like are not suitable for large-scale culture because they allowonly one cell aggregate to be produced in one well. Although the hangingdrop method is widely applied to research, it is not suitable forlarge-scale culture for producing more than several hundred or severalthousand order of cell aggregates at a time.

Non patent literature 4 discloses a method using a low adherencecontainer. Non patent literature 4 also discloses a development of amethod using roller bottle. Further disclosed is a development of amethod for immobilizing cells in a gel or beads so as to carry outsuspension culture. Although these methods enable several thousand cellaggregates to be produced with a high density, there is a problem thatthe produced cell aggregates are heterogeneous. Roller bottles in lowrotation that are capable of large-scale production of comparativelyhomogeneous cell aggregates are being developed. However, these methodsrequire a large-scale apparatus accompanied with complicated operation.Further, even though the rotation speed of roller bottles or the like iscontrolled precisely, any adjacent cells and cell aggregates may beirregularly associated with each other to form another cell aggregatesin a solution. It is thus difficult to produce uniform size cellaggregates.

For example, patent literature 1 discloses an example of a method forproducing a group of cell aggregates in a large number and withconvenience. In this group, morphological features such as size andshape of the cell aggregates and properties outside cells arehomogeneous. In the method disclosed in patent literature 1, a culturesolution containing cells is poured into a hollow part of a structuralmember, wherein at least one lower end of the hollow part is opened. Atthis time, a portion of the culture solution is made to project downwardfrom the open end. In this method, the cells are cultured in theprojecting portion of the culture solution. This method has a problemfor pouring the culture solution into the hollow part when an upper endof the hollow part is closed. Another problem of this method is that aprocess for forming the projecting portion of the culture solution iscomplicated. Moreover, a problem in this process is that it is necessaryto accurately adjust an amount of pouring. Although the pouring(suction)of the culture solution can be efficiently carried out when both ends ofthe hollow part are open, there is another problem in this method. Theproblem is that the upper end needs to be closed or a mechanism formaintaining a suction pressure needs to be further included in order tomaintain a state of the culture solution that has been poured into. Newlimitations are imposed on this manner since an amount of the culturesolution that can be involved in metabolism of the cells is regulated bya volume of the hollow part. One of the new limitations is that a cellconcentration and a culture period are limited by the metabolic activityof a cell for use. The available size of cell aggregates and types ofcells are also limited by this new limitation. Patent Literature 2discloses a suspension plate that allows easier pouring of a culturesolution than that in the technique disclosed in Patent literature 1.Patent literature 2 discloses a structure in which a culture solution iscommunicated from a first surface with a second surface. However, withthe manner disclosed in patent literature 2, the number of pouringoperations is increased in proportion to the number of cell aggregatesto be created. Accordingly, the problem of complicated operations stillremains.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent No. 5074382-   Patent Literature 2: International Patent Publication No. WO    2010/031194

Non Patent Literature

-   Non Patent Literature 1: Kenneth M. Yamada, et al. “Modeling Tissue    Morphogenesis and Cancer in 3D”, Cell 130, Sep. 24, 2007, pp.    601-610-   Non Patent Literature 2: Erik Eschbach et al., “Microstructured    Scaffolds for Liver Tissue Cultures of High Cell Density:    Morphological and Biochemical Characterization of Tissue    Aggregates”, Journal of Cellular Biochemistry 95, 2005, pp. 243-255-   Non Patent Literature 3: C L Bauwens, et al. “Control of Human    Embryonic Stem Cell Colony and Aggregate Size Heterogeneity    Influences Differentiation Trajectories”, Stem Cells 26, 2008, pp.    2300-2310-   Non Patent Literature 4: Sasitorn Rungarunlert, et al. “Embryoid    body formation from embryonic and induced pluripotent stem cells:    Benefits of bioreactors”, World Journal of Stem Cells 1(1), Dec. 31,    2009, pp. 11-21

SUMMARY OF INVENTION Technical Problem

As described above, the conventional culture method using the containerfor the hanging drop method and the culture method using the rotarybottles have advantage and drawback. It has thus been difficult toproduce a large number of cell aggregates that are uniform in shape andsize. Large-scale production, which is several hundred or thousandorder, of such cell aggregates has been particularly difficult.

The present invention has been made in light of the above problems.

Solution to Problem

The present inventors have investigated a physical phenomenon occurringbetween a device for culturing cells and a culture medium. As a resultof the investigation, the present inventors have achieved a device forproducing spheroids with a convenient method.

In an exemplary aspect of the present invention, a spheroid-producingdevice includes at least a first surface, a second surface, and aplurality of wall surfaces. The second surface is a back side surface ofthe first surface. The respective wall surfaces constitute a pluralityof holes penetrating through the first surface and the second surface.In addition, an equivalent diameter of inscribed circles of openings inthe first surface is greater than an equivalent diameter of inscribedcircles of openings in the second surface. According to the aboveexemplary aspect, it is possible to provide a device suitable for easilyproducing a large number of spheroids. This device enables a culturemedium to be poured from the first surface that is disposed on an upperside and produced spheroids to be recovered from the second surface thatis disposed on a lower side. This facilitates seeding process of cellsand culturing process of the cells. It is thus possible to reduce timesrequired for these processes. Additionally, there are followingadvantages in forming holes in the spheroid-producing device in whichthe diameter of the holes is increased from the second surface towardthe first surface. Firstly, a culture solution can be easily infiltratedinto the device from the first surfaces toward the second surface.Secondly, as the density of the settled cells will become greater nearthe second surface, spheroids formation can be promoted. In addition tothe above advantages, it will become easy to manufacture the deviceitself.

In another exemplary aspect of the spheroid-producing device, anequivalent diameter of inscribed circles of openings formed by the holesis preferably greater than a length of an equivalent diameter ofinscribed circles of openings in the second surface. The equivalentdiameter of the inscribed circles of the openings in the second surfaceis preferably within a range of 200 micrometers to 1 cm. At leastportions of the respective wall surfaces preferably include inclinationswith an angle greater than one degree and smaller than 90 degrees withrespect to the second surface. When a hydrophobic material is used, itis preferable to determine an equivalent radius of the circumscribedcircles (a length half of the equivalent diameter) of the openings inthe second surface in consideration of a contact angle between thematerial of the device and the culture medium. When a hydrophilicmaterial is used, it is preferable to determine an equivalent radius ofthe inscribed circles of the openings in the second surface inconsideration of the contact angle between the material of the deviceand the culture medium.

In another exemplary aspect of a method for recovering spheroids thatare produced by using the above mentioned spheroid-producing device, themethod includes bringing the second surface of the spheroid-producingdevice into contact with a solution selected from water, a culturemedium, and a buffer solution in order to recover spheroids.Alternatively, the method includes applying a pressure on the firstsurface of the spheroid-producing device in order for spheroids to beretrieved through the openings in the second surface. According toeither of the recovery methods, it is possible to easily recoverspheroids without damaging the spheroids.

In still another exemplary aspect of a method for producing spheroidsusing the above-mentioned spheroid-producing device, the method includespouring a culture medium containing cells in the respective holes fromthe first surface, forming droplets in the respective holes, andculturing the cells in the droplets in order to produce spheroids. It ispreferable to use the above-mentioned recovery methods in order torecover the spheroids produced by this method.

Advantageous Effects of Invention

The exemplary aspect of the present invention is a spheroid-producingdevice, a method for recovering spheroids, and a method for producingspheroids that are suitable for large-scale production of uniformspheroids by an easy technique. The exemplary aspect of the presentinvention can provide an easy method suitable for producing a largenumber of uniform spheroids.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing showing an example of a spheroid-producing deviceaccording to an exemplary embodiment;

FIG. 2 is a cross-sectional diagram taken along the line 11-11 of thespheroid-producing device shown in FIG. 1;

FIG. 3 is a drawing for explaining details of the spheroid-producingdevice;

FIG. 4 is a drawing showing an example of a cell culture container thatuses the spheroid-producing device according to the exemplaryembodiment;

FIG. 5 is a drawing for explaining forces exerted on a droplet;

FIG. 6 is a drawing for explaining a contact angle between a material ofwall surfaces and a culture medium;

FIG. 7 is a drawing for explaining an angle θ₀;

FIG. 8 is a drawing for explaining a relationship between a liquidsurface and a water pressure;

FIG. 9 is a drawing for explaining a relationship between a liquidsurface and a water pressure when the water pressure is greater thanthat in FIG. 8;

FIG. 10 is a drawing for explaining a relationship between a liquidsurface and a water pressure when the water pressure is greater thanthose in FIGS. 8 and 9;

FIG. 11 is a drawing for explaining surface tension of openings in asecond surface when the liquid surface and the water pressure arebalanced;

FIG. 12 is a drawing for explaining surface tension of openings in thesecond surface when gas and the water pressure are balanced;

FIG. 13 is a drawing for explaining a process for producing spheroids;

FIG. 14 is a drawing for explaining another example of the process forproducing spheroids;

FIG. 15 is a drawing for explaining a method for recovering spheroids(using a culture medium);

FIG. 16 is a drawing for explaining another method for recoveringspheroids (by a pressure);

FIG. 17 is a drawing showing an example of a cross-sectional shape ofthe spheroid-producing device;

FIG. 18 is a drawing showing another example of the cross-sectionalshape of the spheroid-producing device;

FIG. 19 is a drawing showing another example of the cross-sectionalshape of the spheroid-producing device;

FIG. 20 is a drawing showing another example of the cross-sectionalshape of the spheroid-producing device;

FIG. 21 is a drawing showing another example of the cross-sectionalshape of the spheroid-producing device;

FIG. 22 is a drawing showing another example of the cross-sectionalshape of the spheroid-producing device;

FIG. 23 is a drawing showing an example of a shape of openings in thespheroid-producing device;

FIG. 24 is a drawing showing another example of the shape of theopenings in the spheroid-producing device;

FIG. 25 is a drawing showing another example of the shape of theopenings in the spheroid-producing device;

FIG. 26 is a drawing showing another example of the shape of theopenings in the spheroid-producing device;

FIG. 27 is a drawing for explaining a shape of a spheroid-producingdevice used in an example;

FIG. 28 is a cross-sectional diagram taken along the line XXVIII-XXVIIIof FIG. 27;

FIG. 29 is a drawing for explaining a configuration of a cell culturecontainer used in the example;

FIG. 30 is a cross-sectional diagram taken along the line XXX-XXX ofFIG. 29;

FIG. 31 is a photograph of a culture surface before spheroids arerecovered in an example 1;

FIG. 32 is an enlarged photograph of FIG. 31;

FIG. 33 is a photomicrograph of recovered spheroids according to theexample 1 and the comparative example 1;

FIG. 34 is a photograph of a device surface after the spheroids arerecovered in the example 1;

FIG. 35 is a photograph of spheroids according to the comparativeexample 1;

FIG. 36 is a graph showing a particle size distribution according to theexample 1 and the comparative example 1; and

FIG. 37 is a graph showing a particle size distribution when the numberof cells according to the example 1 is changed.

DESCRIPTION OF EMBODIMENTS

Hereinafter, exemplary embodiment will be described with reference tothe drawings. To clarify the description, some parts thereof and some ofthe drawings have been omitted or simplified as appropriate. Note thatin the drawings, elements having the same configuration or function andcorresponding parts are denoted by the same reference signs, andrepeated descriptions will be omitted.

First Exemplary Embodiment

FIG. 1 is an example of a spheroid-producing device according to anexemplary embodiment. FIG. 2 is a cross-sectional diagram taken alongthe line II-II of the spheroid-producing device shown in FIG. 1. Aspheroid-producing device 1 is a device for producing spheroids byculturing cells in a culture medium shaped in a droplet form and thenaggregating cells in order to obtain the spheroids. A spheroid is alarge number of aggregated cells in three dimensions.

The spheroid-producing device 1 includes at least a first surface 11, asecond surface 12, and wall surfaces 13. FIG. 1 is a drawing showing thespheroid-producing device 1 when it is viewed from a side of the firstsurface 11.

The first surface 11 is an upper surface of the spheroid-producingdevice 1 and is a surface that is on an upper side when a culture mediumand the like are poured in order to culture cells.

The second surface 12 is a surface that faces the first surface 11. Thesecond surface 12 forms a bottom (a bottom surface) of thespheroid-producing device 1 and is a back side surface of the uppersurface (the first surface 11).

The wall surfaces 13 form holes (through holes) penetrating through thefirst surface 11 and the second surface 12. Further, the wall surfaces13 serve to form openings in the first surface 11 and the second surface12 and to allow the first surface 11 to communicate with the secondsurface 12.

In addition, in the spheroid-producing device 1, the holes formed by thewall surfaces 13 are designed in such a way that openings thereof formedcloser to the second surface 12 will become smaller than the openingsthereof formed closer to the first surface 11. The sizes of the openingsare compared using an equivalent diameter.

The term “equivalent diameter” is used as a collective term for anequivalent diameter of an inscribed circle and an equivalent diameter ofa circumscribed circle. The “equivalent diameter of the circumscribedcircle” is a diameter of circles circumscribing the openings and is usedas a diameter of the circumscribed circle drawn on a planar surface thatis parallel to the second surface 12. For example, the diameter of thecircumscribed circle drawn on a planar surface parallel to the secondsurface 12 is used as the equivalent diameter of the openings of theholes formed between the first surface 11 and the second surface 12. The“equivalent diameter of the inscribed circle” is a diameter of circlesinscribing the openings and is used as a diameter of the inscribedcircle drawn on a planar surface that is parallel to the second surface12. For example, the diameter of the inscribed circle drawn on theplanar surface parallel to the second surface 12 is used as theequivalent diameter of the openings of the holes formed between thefirst surface 11 and the second surface 12. A length denoted by the sign“D” in the drawings is an equivalent diameter Dout of the circumscribedcircle or an equivalent diameter Din of the inscribed circle. The sign“D” does not make a clear distinction between Dout and Din.

Details of the size of the openings will be described below withreference to FIG. 3.

A configuration of the spheroid-producing device 1 will be described inmore detail with reference to FIG. 3, in addition to FIGS. 1 and 2. FIG.3 is a drawing for explaining details of the spheroid-producing device.FIG. 3 uses the cross-sectional diagram shown in FIG. 2 without theshades indicating the cross sections for easier descriptions.

The spheroid-producing device 1 is designed in consideration of at leastan angle θi, the equivalent diameter Dout of the circumscribed circlesof the openings in the second surface 12 or the equivalent diameter Dinof the inscribed circles of the openings in the second surface 12, amaterial used for the device, and a culture medium 8 used for cellculture. Preferably, a thickness T and a width W may be added to theconsideration.

The angle θi is an angle made by inclined surfaces of the wall surfaces13 make with respect to the second surface 12. At least a portion of theinclined surfaces of the wall surfaces 13 may make the angle θi withrespect to the second surface 12. On the other hand, the entire wallsurfaces 13 that form the holes may not be inclined at the angle θi. Theangle θi is preferably greater than one degree and smaller than 90degrees and more preferably within a range of 30 to 80 degrees. This isto facilitate the culture medium 8 to be poured into the holes.Alternatively, this is for all of seeded cells to settle down to lowerparts of droplets by their own weights without staying on the wallsurfaces 13. It is therefore possible to efficiently culture the cells.

The thickness T is a thickness of the spheroid-producing device 1 fromthe first surface 11 to the second surface 12. The thickness T may bethe one that can bear the weight of the culture medium 8.

The equivalent diameter Dout of the circumscribed circles of theopenings in the second surface 12 is a diameter of circumscribed circlesthat circumscribe the openings formed in the second surface 12.

The equivalent diameter Din of the inscribed circles of the openings inthe second surface 12 is a diameter of circles that inscribe theopenings formed in the second surface 12. Further, an equivalent radiusRout of the circumscribed circles is a half of the lengths of theequivalent diameter Dout of the circumscribed circles. An equivalentradius Rin of the inscribed circles is a half of the lengths of theequivalent diameter Din of the inscribed circles.

In exemplary one embodiment, the equivalent diameter of the inscribedcircles of the openings in the first surface 11 are designed in such away that they will become greater than the equivalent diameter Din ofthe inscribed circles of the openings in the second surface 12.

In addition, the equivalent diameter Din of the inscribed circles of theopenings in the second surface 12 are preferably one to ten times asgreat as a desired size of a spheroid (e.g., 200 μm to 1 cm).Furthermore, the greater the number of holes per unit area, the morecell aggregates can be produced in a small area. Thus, the equivalentdiameter Din of the inscribed circles of the openings in the secondsurface 12 is more preferably one to two times as great as a desireddiameter of a cell aggregate.

The width W of the upper surface is a width between the wall surface 13that constitutes one hole and another wall surface 13 that constitutesanother adjacent hole. Further, the width W of the upper surface is awidth at the position where the wall surface 13 inclined at the angle θiwith respect to the second surface 12 ends. In other words, the two wallsurfaces 13 that constitute the adjacent holes have inclined surfacesfrom the second surface 12 to the first surface 11, and the width W ofthe upper surface can be considered as being a width at an edge thatenables the inclined surfaces to have the angle θi.

FIG. 3 schematically shows a state in which the culture medium 8 ispoured into the holes and a space above the spheroid-producing device 1from the first surface 11 (from the openings in the first surface 11)until a height (a depth) of the culture medium 8 reaches a height (adepth) H. As shown in FIG. 4, this space corresponds to a space inside awell container 91. In the configuration example of thespheroid-producing device 1 shown in FIG. 3, the culture medium 8 ispoured in such a way that the culture medium 8 projects from theopenings in the second surface 12. The portions projecting from thesecond surface 12 are droplets 81. In other words, the culture medium 8is poured into the spheroid-producing device 1 so that the droplets 81are formed. The droplets 81 serve as three-dimensional cell cultureequipment when cells are cultured to be formed into spheroids. Downwardliquid surfaces of the droplets 81 are formed as curved surfaces havinga predetermined radius of curvature. A pressure difference ΔP (P-Pair)between air surrounding the droplets and liquid can be expressed by theYoung-Laplace equation, namely, ΔP=Hρ=γ_(L)(1/r1+1/r2). In thisequation, γ_(L) is surface tension of the liquid [g/cm], and r1 and r2are radii of curvature that are orthogonal to each other. If thesurfaces of the droplets 81 are spherical, r1=r2 is satisfied. As thesecurved surfaces project downward, the droplets 81 are formed.

As a modified example of FIG. 3, when the culture medium 8 is pouredfrom the first surface 11 (from the openings in the first surface 11),the pouring can be adjusted in such a way that the height (the depth) Hof the culture medium 8 will become lower than the above height (theabove depth). In such a case, in the configuration example of thespheroid-producing device 1 shown in FIG. 3, the culture medium 8 ispoured in such a way that the culture medium 8 is poured halfway downthe inclined surfaces (the wall surfaces 13) connecting the openings inthe second surface 12 to the openings in the first surface 11. FIG. 14,which will be described later, schematically shows a state in which theculture medium 8 is poured halfway down the inclined surfaces in orderto culture cells.

Details regarding the design of the spheroid-producing device such asquality of a material used for the device, properties of the culturemedium used for cell culture, the equivalent diameter, and the like willbe described later with reference to the drawings.

Note that in FIG. 3, to be precise, the wall surfaces 13 are surfacesthat maintain the angle θi with respect to the second surface 12.Moreover, inclined surfaces between the first surface 11 and the wallsurfaces 13 may be referred to as upper surfaces. Alternatively, in abroad context of the first surface 11, the first surface 11 may includea surface not parallel to the second surface 12 (an upper surface). Ifthese terms are not concerned with an essence of the exemplaryembodiment of the present invention, no clear distinctions shall be madebetween these terms.

FIG. 4 shows an example of a cell culture container that uses thespheroid-producing device according to the exemplary embodiment. A cellculture container 9 is an example of a basic structure of a cell culturecontainer. In the cell culture container 9, the spheroid-producingdevice 1 is attached to the well container 91. A Petri-dish 92 isdisposed outside the well container 91.

The spheroid-producing device 1 and the well container 91 may be made ofthe same material or materials different from each other. Since the wellcontainer 91 provides the space into which the culture medium 8 ispoured, the well container 91 may be made of any material as long as itis not toxic to the cells. On the other hand, the Petri-dish 92 may bethe one that has a shape that will not be brought into contact with thesecond surface 12 of the spheroid-producing device 1 and the droplets81.

The container to which the spheroid-producing device 1 is attached isnot limited to a structure shown in FIG. 4. When cells are cultured bythe spheroid-producing device 1, the spheroid-producing device 1 may beattached to a multi-well plate or a Petri-dish and then used. Thespheroid-producing device 1 may be used in any way as long as the secondsurface 12 (the bottom surface) and the droplets 81 will not be broughtinto contact with the multi-well plate or the Petri-dish.

Hereinafter, design of the spheroid-producing device will be describedin detail. It is preferable that the following physical phenomenon istaken into consideration when the material and surfaces of thespheroid-producing device 1 and the equivalent diameter Din of theinscribed circles of the openings in the second surface 12 or theequivalent diameter Dout of the circumscribed circles of the openings inthe second surface 12 are designed. In particular, the contact angle θcbetween the material of the wall surfaces 13 and the culture medium 8may be preferably added to the consideration. The reason for that is thecontact angle θc of the spheroid-producing device 1 is influenced byquality of the material used for the device, properties of the culturemedium, and the like. In the following descriptions, firstly the designof the spheroid-producing device 1 in consideration of the physicalphenomenon related to the contact angle θc will be investigated. Afterthat, other elements will be described.

FIG. 6 is a schematic diagram for explaining the contact angle θcbetween the quality of the material that appears on the wall surfaces 13and the culture medium 8. The contact angle θc is a contact angle of aliquid with respect to a solid. The contact angle θc is determined byproperties of the solid and liquid. Further, γ_(S) is surface tension ofthe solid [g/cm], γ_(SL) is solid liquid surface tension [g/cm], andγ_(L) is surface tension of the liquid [g/cm].

The contact angle θc is determined by the properties of the solid andliquid. To be more specific, the contact angle θc is determined byquality of the material used for the spheroid-producing device 1(quality of the material that appears on the wall surfaces 13) and theproperties of the culture medium 8.

<Investigation on Contact Angle θc>(1) The case when the contact angle θc is within a range of −1<cos θc≤0.

In this case, the size of the droplets is not influenced by the contactangle. An allowable range is an angle θ₀=90 degrees.

When the contact angle θc is within a range of −1<cos θc≤0, thespheroid-producing device 1 is commonly regarded as being made of ahydrophobic material. In this regard, the diameters Din of the inscribedcircles of the openings in the second surface 12 are smaller than thediameters of the inscribed circles of the openings in the first surface11. In addition, the size of the equivalent diameter Dout of thecircumscribed circles will become important.

FIG. 5 is a drawing for explaining forces exerted on the droplet 81. InFIG. 5, the shape of the droplet 81 is considered to be hemispherical.The second surface is disposed to be horizontal. In practice, thedroplet 81 is a liquid that is continuous with the culture medium 8 withno boundary between them. In FIG. 5, a range defined as being thedroplet 81 is shaded differently from the culture medium 8 for easierdescriptions.

F0 to F2 are present as the forces exerted on the droplet 81 and forcesworking in parallel to gravity.

F0 is a force of gravity exerted on the droplet 81 and calculated by thefollowing equation.

F0=volume×specific gravity

=V·α

F1 is a force derived from a water pressure of the liquid (the culturemedium 8) exerted on the droplet 81 and calculated by the followingequation.

F1=water pressure×area=pS

In the case of an atmosphere pressure,

F1=depth from upper liquid surface to droplet×density of liquid×area

=HρS

F2 is a force derived from surface tension of a liquid generated at aperiphery of the liquid surface and calculated by the followingequation.

F2=outer circumference×liquid surface tension×angle

=Lγ _(L) sin θ₀

The surface tension of the liquid γ_(L) can be measured by variousmethods such as the Wilhelmy method. Alternatively, the information canbe obtained from the distributor. The contact angle θc can be measuredby measuring the liquid (the culture medium and a buffer solution) andmaterials to be used using the droplet method and the gas-liquid method.

In FIG. 8, γ_(SL) is also related to a condition for a water surface tobe stopped on the wall surface. On the other hand, γ_(SL) is not relatedto a condition for droplets to be held as in FIG. 9. At this time,γ_(SL) is assumed to be acting in a direction of the second surface.

In the above equations, a volume V is a volume [cm³] of the droplets 81,a specific gravity α is a specific gravity of the culture medium 8, aheight H is a height equivalent to a depth [cm] from the upper surfaceof the culture medium 8 to a lower end of the droplet 81, and density ρis density of the culture medium 8 [g/cm].

An area S is a size of an area of an opening at a position where thedroplet 81 is generated (at a position where the droplet is formed inthe hole). In this example, the area S is an area [cm²] of a boundarythat is brought into contact with the second surface 12 and is the sameas an area of the opening in the second surface 12.

A water pressure p is a water pressure [g/cm²] at the opening in thesecond surface 12. A length L of an outer circumference is a length [cm]of a boundary at which the droplet is brought into contact with thesecond surface 12. The length L is equivalent to a length of acircumference of the opening in the second surface. The solid liquidsurface tension γ_(SL) is surface tension (interfacial tension) [g/cm]between the wall surfaces 13 and the culture medium 8. The angle θ₀ isan angle the surface of the droplet 81 makes with a horizontal surfaceor the second surface 12 that is placed horizontally. When the droplet81 is hemispherical in FIG. 5, the angle θ₀=sin 90°=1. The angle θ₀ isan angle a contact surface at a peripheral portion with which thedroplet 81 is in contact makes with a horizontal surface. Alternatively,the angle θ₀ is an angle this contact surface makes with respect to thesecond surface 12 that is placed horizontally. FIG. 7 is a drawing forexplaining the angle θ₀.

When the following equation 1 is satisfied, the droplets 81 are held inthe spheroid-producing device 1.

F0+F1<F2  Equation 1

When the droplets stay on the wall surfaces 13 as shown in FIG. 8, F2can be expressed by the following equation from the above equation.

F2=Lγ _(SL) sin θ_(i) +Lγ _(L) sin θ₀

(where θ_(i) is an inclined angle of the wall surfaces)

Thus, the equation 1 (F0+F1<F2) can be expressed by the followingequation 2.

Vα+pS<Lγ _(SL) sin θ_(i) +Lγ _(L) sin σ₀  Equation 2

Further, when the droplets are continuous with the second surface 12 asshown in FIG. 9, F2 can be expressed by the following equation.

F2=Lγ _(L) sin θ₀

Accordingly, the equation 1 (F0+F1<F2) can be expressed by the followingequation 3.

Vα+pS<Lγ _(L) sin θ₀  Equation 2-2

Assume that the culture medium 8 is poured up to the height H using amaterial having the contact angle θc. When the droplets 81 start tobecome narrow, the droplets 81 start to project outwardly from thesecond surface 12. At this time, F0+F1=F2 is satisfied. The angle θ₀ is90 degrees (sin 90=1).

F0 can be expressed by the following equation, where V is a volume ofthe droplet 81, Rout is the equivalent radius of the circumscribedcircle of the opening in the second surface 12, and a is the specificgravity.

F0=((4/3)πRout³÷2)×α=(2/3)πR ³·α

However, when the droplet 81 is hemispherical, the volume V iscalculated by [(volume of the sphere)÷2].

Further, the following equation is satisfied, when the area of theopening S and the length of the outer circumference L of the opening areexpressed by an equivalent radius R.

S=πRout² , L=2πRout

From the equation 3,

(⅔)Rout³ ·α+pπRout²

=2πRoutLγ _(L) sin 90

In this equation, sin 90=1.

Accordingly,

(⅔)αRout² +pRout=2γ_(L)  Equation 3

That is, the equivalent diameter Rout of the circumscribed circle in theequation 3 is preferably a maximum equivalent radius of the openings inthe second surface 12. The diameters of the openings in the secondsurface 12 are preferably 2Rout or less. It is more preferable to designthe device in consideration of a force (Fc) exerted from gravity on cellaggregates.

As described above, when the contact angle θc is within a range of−1<cos θc<0 (the contact angle is 90 degrees or greater, and θ₀ will notexceed θc), it is preferable that the equivalent diameter Dout of thecircumscribed circles of the openings in the second surface 12 are lessthan or equal to twice the equivalent radius of the circumscribedcircles calculated by the equation 3. With this exemplary embodiment,the droplets can be maintained in the spheroid-producing device 1.

(2) The case when the contact angle θc is within the range of 0<cos θc<1

When the contact angle θc is within the range of 0<cos θc<1, thespheroid-producing device 1 is commonly regarded as being made of ahydrophilic material. The equivalent diameter of the inscribed circlesare used in designing the size of the openings 12 in the second surfacewhen such a material is used.

A relationship between the liquid surface and water pressure will bedescribed with reference to FIGS. 8 and 9. When a water pressure p1 inFIG. 8 is used as a reference, FIG. 9 shows a case in which a waterpressure p2 is greater than the water pressure p1 of FIG. 8 (p1<p2).FIG. 10 shows a case in which a water pressure is greater than the waterpressures in FIGS. 8 and 9 (p1<p2<p3). FIG. 8 shows a state in which themagnitude of the water pressure p1 and the liquid surface are balanced,and in which the liquid will not fall down and is stopped. FIG. 9 showsa state in which the liquid surface is closer to the second surface 12as compared to the state in FIG. 8 because the water pressure p2 isgreater than the water pressure p1. In FIG. 9, the magnitude of thewater pressure P2 and the liquid surface are balanced. The greater theheight H in FIG. 5 (the more the amount of the culture medium 8), thegreater the water pressure becomes. As a result, when θ₀ exceeds thecontact angle θ_(c), a triple line at which the liquid, the device, andair are brought into contact with one another moves as shown in FIG. 10.Thus, the liquid surface comes around the openings in the second surface12 and is adhered to the second surface 12. In the state shown in FIG.10, the liquid is continuously supplied from above thespheroid-producing device 1. As a result, the droplets are enlarged anddrop, thereby making it difficult to stably hold one droplet in eachhole. That is, the state shown in FIG. 8 or 9 is preferable.

Therefore, it is preferable to design the spheroid-producing device 1 sothat the following conditions are satisfied. FIG. 12 is a drawing forexplaining surface tension at the opening in the second surface 12 whenthe liquid surface and the water pressure are balanced. FIG. 11 shows acase when the surface tension is adjusted to achieve the state of FIG.9.

A condition for avoiding the state of FIG. 10 is that the surfacetension of the solid γ_(S) does not exceed a sum of the solid liquidinterfacial tension T_(SL) and the surface tension of the liquid surface(γ_(L) cos θ₀).

That is,

γ_(S)≤γ_(L) cos θ₀  Equation 5

In comparison between the equation 5 and the Young equation(γ_(S)=γ_(SL)+γ_(L) cos θ_(c)), when θ₀≤θ_(c) is satisfied, droplets arestably maintained.

FIG. 6 is a schematic diagram for explaining the contact angle θcbetween the material of the wall surfaces 13 and the culture medium 8.The contact angle θc is a contact angle of the liquid with respect tothe solid and determined by properties of the solid and liquid. In theequations, γ_(S) is the surface tension of the solid [g/cm], γ_(SL) isthe solid liquid surface tension [g/cm], and γ_(L) is the surfacetension of the liquid [g/cm].

The contact angle θc is determined by the properties of the solid andliquid, and more specifically, determined by the materials (thematerials of the second surface 12 and the wall surfaces 13) of thespheroid-producing device 1 and the properties of the culture medium 8.

The surface tension γ_(SL) of the solid is preferably obtained on theInternet (http://www.surface-tension.de/solid-surface-energy.htm) orobtained from a distributor etc. Alternatively, the surface tensionγ_(SL) of the solid may be calculated using the Zisman method. Thesurface tension of the liquid γ_(L) can be measured by various methodssuch as the Wilhelmy method. Alternatively, the information can beobtained from a distributor. The contact angle θc can be measured bymeasuring the liquid (the culture medium and a buffer solution) andmaterials to be used using the droplet method and the gas-liquid method.Thus, γ_(SL) can be derived by substituting the values of γ_(L) andγ_(S) into the equation of γ_(SL)=γ_(L) cos θc−γ_(S).

Therefore, the equation 5 is;

γ_(S)≤γ_(L) cos θc−γ _(S)+γ_(L) cos θc

γ_(L) cos θc−γ _(S)≥0  Equation 6

As shown in FIG. 12, as to the downward liquid surface of the droplets81, a pressure difference ΔP(P-Pair) between air and liquid surroundingthe droplets in accordance with the Young-Laplace equation can beexpressed as:

ΔP=p=γL(1/r1+1/r2)  Equation 7

In the case of an atmospheric pressure, it is expressed by the followingequation.

ΔP=Hρ=γL(1/r1+1/r2)  Equation 7-2

The droplets have curved surfaces and project downwardly. In thisequation, γ_(L) is the surface tension of the liquid [g/cm], and r1 [cm]and r2 [cm] are radii of curvature that are orthogonal to each other atone point on the surface.

When the surfaces of the droplets 81 are spherical, r1=r2 is satisfied.Thus,

p=γL×(2/r)  Equation 8

In the case of an atmospheric pressure, it is expressed by the followingequation.

Hρ=γL×(2/r)  Equation 8-2

As described above, from the moment when the droplets flow over thesecond surface 12, it will be difficult to hold the droplet. In view ofthe above, with the contact angle θc that is within a range of 0<cosθc<1, a relationship between conditions when θ₀=θ_(c) and the equivalentdiameter Din of the inscribed circles of the openings in the secondsurface 12 will be examined with reference to FIG. 12.

When the culture medium with properties of ρ and γ_(L) is poured up tothe height H [cm] using a material with a property of γ_(S) under anatmospheric pressure, a material that satisfies cos θc>γ_(S)/γ_(L),which is derived from the equation 6, is selected.

A vertical auxiliary line is drawn down from a center of a circle thatis estimated from the radius of curvature, the following equation issatisfied.

Din=2r−sin θ₀

From the equation 8-2, as r=2HργL, it can be expressed by the followingequation.

Din=4·γL−sin θ₀ /Hρ  Equation 9

When a limit at which the droplets can flow over the second surface 12,which is when θ₀=θ_(c) is substituted into the above equation, a maximumdiameter Din (max) of the inscribed circles that can hold the dropletsis expressed by the following equation.

Din(max)=4·γL·sin θ_(c) /Hρ  Equation 9-2

That is, it is preferable to design the device in such a way that thediameters of the inscribed circles will be smaller than the valuecalculated by the above formula.

When the device is designed under such conditions, regardless of thecontact angle θc (i.e., whether the material of the device ishydrophobic or hydrophilic), it is preferable to consider absorption ofprotein contained the culture medium into the material when the deviceis designed. It is thus preferable that the size of the openings in thesecond surface 12 is a value within a range of 20 to 80% of a maximumvalue of the calculated equivalent radius R. Further, it is preferableto adjust the height H of the culture medium 8 in such a way that awater pressure derived from the height H of the culture medium 8 will bewithin a range of 50 to 80% of the calculated maximum water pressure pin order to adjust the amount of the culture medium.

As described above, it is possible to manufacture the spheroid-producingdevice 1 in which droplets are appropriately formed by designing theequivalent diameter Din of the inscribed circles and the equivalentdiameter Dout of the circumscribed circles according to the contactangle θc. In other words, it is possible to design and produce thespheroid-producing device 1 according to the material used for thespheroid-producing device 1 and the properties of the culture medium 8used for cell culture. As the droplets suitable for cell culture can beformed by the spheroid-producing device 1, it is expected that a largenumber of spheroids can be efficiently produced using thespheroid-producing device 1. In addition, it is expected that uniformspheroids be produced by forming appropriate droplets using thespheroid-producing device 1.

Note that in the above (1) to (3), the equations used to design thespheroid-producing device 1 according to the range in which the value ofthe contact angle θc can be included have been presented. This isbecause it is preferable to test several design methods according to thematerial of the spheroid-producing device 1 or the properties of theculture medium 8. Further, this is because the spheroid-producing device1 is designed and manufactured using preferable equation(s) asappropriate.

<Width of Upper Surface>

A width W of the upper surface of a wall that partitions spaces ispreferably 5 mm or less. More preferably, the width W is 2 mm or less sothat cells will not stay or stand still on the upper surface (on thefirst surface 11 and near the first surface 11). It is preferable toconsider a shape of the upper surface (a shape of an upper portion fromthe first surface 11 to the width of the upper surface) together withthe width W of the upper surface. This will be described later in detailwith reference to FIGS. 17 to 22.

<Material of Spheroid-Producing Device>

The spheroid-producing device 1 is preferably a resin molding made ofone of or a combination of acrylic resin, polylactic acid, polyglycolicacid, styrene resin, acrylic-styrene copolymer resin, polycarbonateresin, polyester resin, polyvinyl alcohol resin, ethylene-vinyl alcoholcopolymer resin, thermoplastic elastomer vinyl chloride resin, siliconeresin, and silicon resin. This is because resin that can be molded isused in order to manufacture devices at a low cost and in large numbers.

Further, when the spheroid-producing device 1 is the above-mentionedresin molding, it is preferable to form functional groups at least onthe wall surfaces 13 by the surface modification treatment, which is oneof or a combination of plasma treatment, corona discharge, and UV ozonetreatment. Functional groups may be formed on the entirespheroid-producing device 1. This is because when the device is toohydrophobic or when the openings are too small, providing the devicewith a hydrophilic property enables a culture medium to be smoothlypoured into the openings.

Furthermore, when the spheroid-producing device 1 is the above-mentionedresin molding, it is preferable that at least the wall surfaces 13 arecoated with a substance made of one of or a combination of inorganicsubstances, metal, synthetic polymers, dimers, trimers, tetramers, andbiobased polymers. Alternatively, the entire spheroid-producing device 1may be coated with these substances. The reason for this is the same asthe one described above. Additionally, it is extremely effective to coatthe surface with the above material(s) and to thereby form a hydrophobicsurface. This is because when a culture medium having low surfacetension is used, a hydrophobic surface of the device is more effectivethan a hydrophilic surface of the device, provided that both of thedevices have holes with the same equivalent diameter.

Moreover, it is preferable that the spheroid-producing device 1 is amolding made of one of or a combination of inorganic substances such asmetal and glass. When the spheroid-producing device 1 is theabove-mentioned molding, it is preferable to modify at least the wallsurfaces 13 by the surface modification treatment, which includes one ofor a combination of plasma treatment, corona discharge, and UV ozonetreatment. The entire surface of the spheroid-producing device 1 may bemodified. The reason for this is the same as the one described above.Additionally, it is extremely effective to create a more hydrophobicsurface by coating the surface with the above-mentioned material. Thisis because when a culture medium having low surface tension is used, ahydrophobic surface of the device is more effective than a hydrophilicsurface of the device, provided that both of the devices have holes withthe same equivalent diameter.

Alternatively, when the spheroid-producing device 1 is theabove-mentioned molding, at least the wall surfaces 13 are coated with asubstance made of one of or a combination of inorganic substances,metal, polymer, diners, trimers, and tetramers. The entirespheroid-producing device 1 may be coated with these substances. Thereason for this is the same as the one described above. Additionally, itis extremely effective to create a more hydrophobic surface by coatingthe surface with the above-mentioned material. This is because when aculture medium having low surface tension is used, a hydrophobic surfaceof the device is more effective than a hydrophilic surface of thedevice, provided that both of the devices have holes with the sameequivalent diameter.

In addition to the above processing, at least the front surfaces of thewall surfaces 13 or the entire spheroid-producing device 1 preferablyincludes nanometer order microstructures. The microstructures are, forexample, structures with their front surfaces processed to have unevensurfaces. Properties of the material front surface are not specified bythe material of the device but are specified by the properties of thematerial front surface. As hydrophilicity/hydrophobicity of the frontsurface of the material can be controlled in aftertreatment, anymaterial may be used as a material for the device.

<Method for Recovering Spheroids>

An outline of a method for producing spheroids using the above-mentionedspheroid-producing device 1 and a method for recovering the producedspheroids will be described below.

FIG. 13 is a drawing for explaining processes for producing spheroidsusing the cell culture container 9 shown in FIG. 4. The culture medium 8containing cells is poured into respective holes in thespheroid-producing device 1 from the side of the first surface 11. Ifthe spheroid-producing device 1 is designed appropriately as describedabove, the culture medium 8 projects from a bottom of thespheroid-producing device 1 (the openings in the second surface),thereby forming droplets of the culture medium. The cells contained inthe culture medium 8 are aggregated in the droplet portions and formspheroids 7. During cell culture, for example, a supernatant of theculture medium 8 is extracted, and the culture medium 8 is exchangedwith a new culture medium by being supplemented with the new culturemedium.

FIG. 14 is a drawing for explaining another example of processes forproducing spheroids using the cell culture container 9 shown in FIG. 4.FIG. 14 is a drawing showing a state in which droplets do not reachopenings in the second surface 12 and are stopped halfway down theopenings. Such a phenomenon occurs when a culture medium is added up toa height lower than the height H, which has been designed, into thespheroid-producing device 1 that is appropriately designed as describedabove. Even in such a case, cells contained in the culture medium 8 areaggregated in the droplet portions to form the spheroids 7. During cellculture, for example, a supernatant of the culture medium 8 isextracted, and the culture medium 8 can be exchanged with a new culturemedium by being supplemented with the new culture medium. In order torecover spheroids, the culture medium is added from the side of thefirst surface 11 so as to increase H or a pressure on the side of thefirst surface is increased, so that the state shown in FIG. 14 isachieved, and then spheroids can be recovered by the method shown inFIG. 15 or 16.

The produced spheroids 7 are recovered by, for example, the methodsshown in FIGS. and 16. The spheroids 7 can be recovered without damagingthe spheroids 7 by the methods described below.

FIG. 15 shows a method for recovering the spheroids 7 by placing arecovery solution in the Petri-dish 92 and bringing the recoverysolution into contact with the second spheroids 7. The recovery solutioncan be selected from any one of, for example, the culture medium 8,water, and a buffer solution. The spheroids 7 that are produced byculturing the cells using the spheroid-producing device 1 are extractedby this method. A preferred exemplary embodiment of this method iscollecting the spheroids by moving the droplets to a side of therecovery solution. It is particularly preferable to bring the dropletsformed on the side of the second surface 12 into the recovery solutionwhen the droplets are moved.

FIG. 16 shows a method for recovering the spheroids 7 by applying apressure from the side of the first surface 11 while the cell culturecontainer 9 is closed with a lid 93. When a pressure is applied from theside of the first surface 11, the droplets are destroyed. As a result,the culture medium 8 flows out in the Petri-dish 92 to thereby enablethe spheroids 7 to be recovered. It is preferable to destroy thedroplets in a manner described above when spheroids cultured using thespheroid-producing device 1 are extracted. Any method may be used toapply a pressure from the side of the first surface 11 in order todestroy the droplets. For example, the culture medium 8 may be addeduntil the droplets are destroyed. Alternatively, the side of the firstsurface 11 is sealed and gas is supplied in order to apply a pressure.

As described above, with the spheroid-producing device 1 according tothis exemplary embodiment, it is possible to generate droplets in aplurality of holes and to produce spheroids. It is thus possible toefficiently produce a large number of spheroids. When the size of theplurality of holes is formed to be the same, uniform spheroids can beproduced. In addition, a culture medium can be poured from the side ofthe first surface 11 (the upper side) into the spheroid-producing device1. Further, the culture medium can be exchanged from the side of thefirst surface 11. Accordingly, an operation of the spheroid-producingdevice 1 is easy. Furthermore, a structure of the spheroid-producingdevice 1 can be simple by designing the spheroid-producing device 1based on the physical phenomenon. It is thus possible to easilymanufacture the spheroid-producing device 1 itself compared to thesuspension plate disclosed in patent literature 2. Consequently, it ispossible to greatly reduce a cost and a working time for producingspheroids.

Second Exemplary Embodiment

In the first exemplary embodiment, although the spheroid-producingdevice 1 having shapes of the holes shown in FIGS. 1 and 2 has beendescribed, the shapes of the holes are not limited to them. For example,the spheroid-producing device 1 a to 1 f having cross sections shown inFIGS. 17 to 22, respectively, instead of the cross section shown in FIG.2, may be employed. In a manner similar to the device shown in FIG. 2,the devices for producing spheroids 1 a to 1 c are examples in which thewall surfaces 13 are formed from boundaries with the second surfaces 12with inclined surfaces having the angle θi. On the other hand, thespheroid-producing device 1 d shown in FIG. 20 is an example in whichthe inclined surfaces with the angle start halfway on the wall surfaces13.

The shapes of the upper surfaces may be, as shown in the examples ofFIGS. 2 and 17 to 22, portions of spheres (FIGS. 2 and 20 to 22),respectively, or flat (FIG. 19). Alternatively, the shapes of the uppersurfaces may be cones or polygonal cones having vertexes (FIGS. 17 and18). In one exemplary embodiment of the spheroid-producing device, morepreferably, the shapes of the upper surfaces are round or are cones orpolygonal cones having vertexes in order to prevent cells from stayingor standing still on the upper surfaces. In addition, the shapes of theupper surfaces may be vertical from the openings in the first surface 11to entries of the holes and have inclined portions only near theopenings in the second surface 12, which are not shown in the drawings.

The spheroid-producing device 1 d shown in FIGS. 20 to 22 will bedescribed below. The equivalent diameter D and the angle θi are anequivalent diameter and an angle, respectively, at the position wherethe device is brought into contact with the culture medium at theopening in the second surface 12 of the device. The shape of the devicemay be those shown in FIGS. 20, 21, and 22. FIG. 20 is a drawing showinga case in which the wall surfaces 13 from the level 2 to 3 have angles.In FIG. 20, the equivalent diameter of the inscribed circles of theopenings at the level 3 is the same as the equivalent diameter of theinscribed circles at the level 4. In this case, the position at thelevel 4 is a reference for the equivalent diameter Din of the inscribedcircles and the angle θi. FIG. 21 is a drawing showing an example inwhich the wall surfaces 13 from the level 3 to 4 have angles. In FIG.21, the equivalent diameter of the inscribed circles of the opening atthe level 3 is greater than the equivalent diameter D of the inscribedcircles at the level 4. In this case, the position at the level 4 is areference for the equivalent diameter Din and the angle θi of theinscribed circles. At this time, inclinations of the wall surfaces 13from the level 3 to 4, namely the angle θi, are preferably smaller thaninclinations of the wall surfaces 13 from the level 2 to 3.

Alternatively, as shown in FIG. 22, the wall surfaces 13 from the level2 to 3 may have angles. In this case, the equivalent diameter of theinscribed circles of the opening at the level 4 is greater than theequivalent diameter of the inscribed circles of the opening at the level3. At this time, the lowest level at which the wall surfaces 13 arebrought into contact with the culture medium is the level 3. Therefore,inclinations from the level 2 to 3 have the angle θi, and the positionsat the level 3 are the equivalent diameter Din of the inscribed circles.In FIGS. 20 to 22, the angles θi are angles at the part of openings inthe second surface (the lower surface) or the side of the second surfacewherein the part contacts with the liquid surface.

In the first exemplary embodiment, cases in which the openings formed inthe first surface 11 and the second surface 12 shown in FIGS. 1 and 2are circular have been explained. However, the shapes of the openingsare not limited to this. For example, devices for producing spheroids 1g to 1 j with openings having shapes shown in FIGS. 23 to 26,respectively, may be employed. As has been described with reference toFIGS. 1 and 2, the spheroid-producing device 1 preferably includes thefirst surface 11 (the upper surface), the openings in the first surface11, and the openings in the second surface 12 (the lower surface) asportions that are brought into contact with the culture medium. Further,the equivalent diameter of the inscribed circles of the openings in thefirst surface 11 is preferably greater than the equivalent diameter Dinof the inscribed circles of the openings in the second surface 12. Thus,the shapes of the holes may be, as indicated by the devices forproducing spheroids 1 g to 1 j, circles or polygons such as rectanglesor octagons. Further, the shapes of the openings in the first surface 11may differ from the shapes of the opening in the second surface 12. InFIGS. 23 to 26, the openings in the first surfaces 11 (or the shapes ofthe openings at the position of the width W of the upper surface) aredenoted by solid lines. The openings in the second surfaces are denotedby dotted lines. These openings are shown as four holes when the devicesfor producing spheroids 1 g to 1 j are viewed from the side of the firstsurfaces 11.

In addition, in one exemplary embodiment of the spheroid-producingdevice, for example, holes may be created by punching a thin sheet-likefilm or a mold may be created, into which resin is poured, and then theresin may be molded into the device. In this regard, the equivalentdiameter of the inscribed circles of the openings in the upper surfaceis made to be greater than the equivalent diameter Din of the inscribedcircle of the openings in the lower surface. Moreover, a support(s) forreinforcing the film or resin may be included in order to support theweight of the culture medium. When the thickness of the film or resin isincreased, the device may be hollowed out in order to reduce the weightof the device.

EXAMPLE

A test for producing spheroids was carried out. Firstly, aspheroid-producing device 1 x having the shapes shown in FIGS. 27 and 28was designed and manufactured. Next, the spheroid-producing device 1 xwas attached to a well container 91 x shown in FIGS. 29 and 30. The wellcontainer 91 x shown in FIGS. 29 and 30 including the spheroid-producingdevice 1 x was attached to a 6-well plate (not shown). At this time, itwas confirmed that droplets 81 and the second surface 12 are not incontact with a bottom of the well plate.

FIG. 27 is a drawing showing the device when it is viewed from the firstsurface. FIG. 28 is a cross-sectional diagram taken along the lineXXVIII-XXVIII of FIG. 27. FIG. 29 is a drawing of the device when it isviewed from the first surface. FIG. 30 is a cross-sectional diagramtaken along the line XXX-XXX of FIG. 29.

The spheroid-producing device 1 x was manufactured with the followingsize in which one pitch PI is 1.00 mm.

Equivalent diameter D of second surface 12 x: 0.25 mmAngle θi: 67.5 degrees

Thickness T: 0.74 mm

Width W of upper surface: 0.184 mm

The size of the well container 91 x is shown below.

Diameter of inner circumference of well container L1: 31 mmHeight of well container L3: 1.5 cm

1. Culture Container Example 1

A material having a contact angle θc within a range of −1<cos θc<0 wasused. Silicone (manufacturer: KCC and grade: SL7260) was used as amaterial for the spheroid-producing device. As the culture medium, 10%FBS added DMEM/F12 was used. Hereinafter, the culture medium will bereferred to as a culture medium A.

<Design of Spheroid-Producing Device>

The above-mentioned equation 3 (which is mentioned again below) wasused.

(⅔)αR ² +pR=2γ_(L)  Equation 3

In this example, the design was carried out under a condition of usingpure water.

-   -   Density and specific gravity of pure water: 1.00 (literature        value)    -   Surface tension of a liquid γ_(L):7×10⁻² [g/cm]

The surface tension γ_(L) of the liquid of the culture medium A can bemeasured by various methods such as the Wilhelmy method. Alternatively,the information can be obtained from a distributor. The contact angle θcof the pure water with respect to the material of the device measuredusing the droplet method was 91 degrees (cos 91 degrees=−0.017). Notethat the culture medium and the pure water used in this example exhibita value of the contact angle θc that is close to the above value.

-   -   The height H of the culture medium was designed in such a way        that it is within 1 cm.

When the culture medium A is used, the above values are substituted intothe equation 3 in order to calculate the equivalent radius Rout of thecircumscribed circles.

(⅔)×1.00×R ²+1×1.00×R=2×7×10⁻²

R=0.123,−1.629

As the equivalent radius Rout of the circumscribed circles is a positivevalue, the following value was defined.

R=0.123 cm=1230 μm

The equivalent diameter Dout of the circumscribed circles was 285 μmthat is 23% of the calculated value. At this time, reduced hydrophobicproperties caused by absorption of protein, a force from a gravity ofspheroids, and possibility that the droplets cannot be held due toculture medium exchange or a media exchange were considered. The angleθi was 67.5 degrees. Further, the openings were designed in such a waythat the size of which will become 1 mm. As shown in FIG. 14, it hasbeen designed in such a way that the device can surely hold the dropletsby causing the droplets to be stopped halfway of lateral surfaces of thedevice. It was designed such that the diameter of 91 x in FIG. 30 willbecome 31 mm.

Comparative Example 1

A low adhesion container, which was obtained by pasting a silicone resin(KE-1603(A/B) manufactured by Shin-Etsu Chemical Co., Ltd. on a bottomof a glass Petri-dish with a diameter of 5 cm was used.

2. Culture Method

(1) A cell suspension that has been adjusted to contain 2.5 millionmouse ES cells in a culture medium of 10 mL was added in a well shown inFIG. 30. These cells were cultured for two days. This cell suspensionwas used in both of the example and the comparative example. Note thatwhen this cell suspension was used, the number of cells that can bepoured into one opening is 1250 per opening. In other examples, the cellsuspensions that have been adjusted in such a way that the number ofcells poured into one opening will become 1500, 1000, and 500,respectively, were used. In these examples, the cells were cultured fortwo days in a manner similar to the above example.(2) In the example, the second surface 12 was brought into contact withthe culture medium, and spheroids were recovered and then observed. Inthe comparative example, the cell suspension was not transferred toanother container, and spheroids were observed in the culturedcontainer.(3) Spheroids were observed by an inverted microscope, and diametersthereof were measured using an obtained image.

3. Result

FIGS. 31 and 32 are photomicrographs of the device and cells before thespheroids are recovered in the example 1. FIG. 32 is an enlargedphotomicrograph of FIG. 31. In the example 1, spheroids were formed inthe respective openings.

FIG. 33 is a photomicrograph of the recovered spheroids according to theexample 1 and the comparative example 1.

FIG. 34 is a photograph of a surface of the device after the spheroidswere recovered in the example 1. Almost all of the remaining spheroidsshown in FIG. 31 were recovered. However, there were still somespheroids remaining at the edge. The recovery rate was 95% or greater.The recovery rate was calculated by the equation (the number of openingsnot including cells/the total number of openings)×100.

FIG. 35 is a photograph of the spheroids in the comparative example 1.

FIG. 36 is a graph showing a particle size distribution according to theexample 1 and the comparative example 1. To create the graph of FIG. 36,the spheroids were photographed using the x75 lens of FIG. 33(photograph in the example 1 on the left and the photograph in thecomparative example 1 on the right), and images of the spheroids werecaptured. The number of pieces of data shown in the following table 1was selected from the captured images, and diameters of the respectivespheroids were measured.

An average value (μm), sample standard deviation (SD), and variations(that is defined by dividing SD by the average value of the diameters)of the diameters of cell aggregates are shown in the table 1. As can beseen from the value of SD/average diameter, variations in the example 1were ⅓ or less of variations in the comparative example 1.

TABLE 1 Average Number SD/Average diameter (μm) SD of data diameter (%)Example 163.4 17.1 98 10.5 Comparative example 77.9 26 100 33.4

FIG. 37 shows a particle size distribution with different number ofcells of the example 1.

An investigation was carried out as to whether or not cell aggregateswith a uniform diameter can be formed even with different number ofcells. Table 2 shows a result of the investigation. With the equivalentdiameter D designed this time, in the cases of 1500 and 1000 cells peropening, variations were about 10% lower than those in the comparativeexample. In the case of 500 cells per opening, the variations werecomparable to those in the comparative example.

TABLE 2 Average Number SD/Average diameter (μm) SD of data diameter (%)1500 cells/opening 225 52.5 554 23 1000 cells/opening 201 47.1 673 23500 cells/opening 143 49.9 717 35

Note that the present invention is not limited by the above exemplaryembodiments, and modifications can be made as appropriate withoutdeparting from the scope of the invention.

The present application is based upon and claims the benefit of priorityfrom Japanese Patent Application No. 2014-034577, filed on Feb. 25,2014, the entire contents of which are hereby incorporated by reference.

REFERENCE SIGNS LIST

-   1, 1 a to 1 h, 1 x SPHEROID-PRODUCING DEVICE-   7 SPHEROID-   8 CULTURE MEDIUM-   9 CELL CULTURE CONTAINER-   11, 11 x FIRST SURFACE-   12, 12 x SECOND SURFACE-   13, 13 x WALL SURFACE-   9 CELL CULTURE CONTAINER-   91, 91 x WELL CONTAINER-   92 PETRI-DISH-   93 LID

1-19. (canceled)
 20. A spheroid-producing hanging drop devicecomprising: a top surface that forms an upper surface of thespheroid-producing device: a bottom surface that is a back side surfaceof the first surface, and that forms a bottom surface of thespheroid-producing device; a plurality of wall surfaces extending fromthe top surface to the bottom surface that define a plurality of wells,each of the plurality of wells having a hole penetrating through the topsurface through which cells and media are introduced into each of theplurality of wells, and a hole penetrating through the bottom surface;wherein a width of the top surface between adjacent wall surfacesdefining one of the wells is 2 mm or less; wherein the top surfacebetween adjacent wells are round or conical or are polygonal coneshaving vertexes; and wherein the plurality of wall surfaces arehydrophilic such that a contact angle θc between the plurality of wallsurfaces and a culture medium disposed in the plurality of wells iswithin a range of 0<cos θc<1, as measured by the droplet method.
 21. Thespheroid-producing hanging drop device according to claim 20, whereinthe holes in the bottom surfaces of the wells are circular, and thediameter of the circular holes in the bottom surfaces of the wells iswithin a range of 200 micrometers to 1 cm.
 22. The spheroid-producinghanging drop device according to claim 20, wherein at least portions ofthe wall surfaces are inclined between the top surface and the bottomsurface, and make an angle greater than 1 degree and smaller than 90degrees with respect to the bottom surface.
 23. The spheroid-producinghanging drop device according to claim 21, wherein a radius (cm) of thecircular holes in the bottom surfaces of the wells is less than or equalto a value of a variable X that is defined by an equation of(⅔)αX ² +pX=2γ_(L), where p is a water pressure [g/cm²] at the openingsin the second surface, α is a specific gravity of the culture medium,and γ_(L) [g/cm] is surface tension of the culture medium as measured bythe Wilhelmy method.
 24. The spheroid-producing hanging drop deviceaccording to claim 21, wherein a diameter of the circular holes in thebottom surfaces of the wells is such that the following equations aresatisfied:γ_(L) cos θc−γ _(S)>0and p=γ _(L)×(2/r) where p is a water pressure [g/cm²] at the openingsin the second surface, γ_(L) is surface tension of the liquid medium[g/cm] as measured by the Wilhelmy method, r is a radius of curvature[cm], and γ_(S) is surface tension of the plurality of wall surfaces[g/cm].
 25. The spheroid-producing device according to claim 22, whereina width between one of the wall surfaces constituting one of the holesand another one of the wall surfaces constituting another adjacent oneof the holes is 5 mm or less, wherein the width is a width of an endportion that is close to the first surface, in which the two wallsurfaces incline at the angle θi with respect to the second surface. 26.The spheroid-producing hanging drop device according to claim 20,wherein the spheroid-producing device is made of a material selectedfrom the group consisting of acrylic resin, polylactic acid,polyglycolic acid, styrene resin, acrylic styrene copolymer resin,polycarbonate resin, polyester resin, polyvinyl alcohol resin,ethylene-vinyl alcohol copolymer resin, thermoplastic elastomer vinylchloride resin, silicone resin, silicon resin, and combinations thereof.27. The spheroid-producing hanging drop device according to claim 26,wherein the plurality of wall surfaces comprise functional groups formedby a surface modification treatment selected from the group consistingof plasma treatment, corona discharge, UV ozone treatment, andcombinations thereof.
 28. The spheroid-producing hanging drop deviceaccording to claim 26, wherein the plurality of wall surfaces are coatedwith a substance selected from the group consisting of inorganicsubstances, metal, synthetic polymers, dimers, trimers, tetramers,biobased polymers, and combinations thereof.
 29. The spheroid-producinghanging drop device according to claim 27, wherein a portion of the wallsurfaces comprise nanometer order microstructures.
 30. Thespheroid-producing device according to claim 20, wherein thespheroid-producing device is a molding made of one of or a combinationof inorganic substances.
 31. The spheroid-producing device according toclaim 30, wherein surfaces of the plurality of wall surfaces aremodified by a surface modification treatment selected from the groupconsisting of plasma treatment, corona discharge, UV ozone treatment,and combinations thereof.
 32. The spheroid-producing device according toclaim 30, wherein the plurality of wall surfaces are coated with asubstance selected from the group consisting of inorganic substances,metal, polymer, dimers, trimers, tetramers, and combinations thereof.33. The spheroid-producing device according to claim 20, wherein frontsurfaces of the plurality of wall surfaces comprise nanometer ordermicrostructures.
 34. The spheroid-producing hanging drop deviceaccording to claim 20, wherein the outer wall surrounding the firstsurface is a part of a well container.
 35. A method for recoveringspheroids from the spheroid-producing device according to claim 20,comprising bringing the second surface of the spheroid-producing deviceinto contact with a solution selected from water, a culture medium, anda buffer solution in order to recover the spheroids.
 36. A method forrecovering spheroids from the spheroid-producing device according toclaim 20, comprising applying a pressure on the first surface of thespheroid-producing device, whereby the spheroids fly out of the openingsin the second surface.
 37. A method for producing spheroids using thespheroid producing device according to claim 20, the method comprising:pouring a culture medium containing cells into the plurality of holesfrom the first surface; forming droplets in the plurality of holes; andculturing the cells in the droplets in order to produce the spheroids.38. The method according to claim 37, further comprising bringing thesecond surface into contact with a solution selected from one of water,a culture medium, and a buffer solution in order to recover thespheroids.
 39. The method according to claim 37, further comprisingapplying a pressure on the first surface to thereby destroy the dropletsand to cause the spheroids to fly out of the openings in the secondsurface.